1. Field of the Invention
The present invention relates to a portable Internet system or mobile Internet system, and more particularly to a method for allowing a mobile communication terminal to stably and effectively re-transmit a handover request message to a base station when the base station has rejected the handover request message of the mobile communication terminal. The present invention also relates to a mobile communication terminal using this method.
2. Discussion of the Related Art
A portable Internet is indicative of the next-generation communication scheme capable of further assigning the mobility to a local-area data communication scheme designed to use a fixed access point in the same manner as in a conventional wireless LAN. In association with the above-mentioned portable Internet, a plurality of standards are being rapidly proposed and introduced to the market. There are a variety of International standards associated with the portable Internet, for example, the IEEE 802.16 standard, and the IEEE 802.20 standard, etc. A portable Internet system will hereinafter be described with reference to the IEEE 802.16 standard.
FIG. 1 is a conceptual diagram illustrating a portable Internet system according to a related art. Referring to FIG. 1, the portable Internet system includes mobile communication terminals (also called mobile stations) 10 and 11, base stations 20 and 21 for wirelessly communicating with the mobile communication terminals 10 and 11, routers 30 and 31 for accessing the base stations 20 and 21 via a gateway, and the Internet 40.
The portable Internet system proposed by the IEEE 802.16 group and other groups guarantees the mobility of the mobile communication terminal 10 although the mobile communication terminal 10 moves from a first cell managed by the base station 20 to a second cell managed by the other base station 21, such that it can provide a user of the mobile communication terminal 10 with a seamless data communication service.
The portable Internet system supports the handover of the mobile communication terminals 10 and 11 in the same manner as in the mobile communication service, and allocates a dynamic IP (Internet Protocol) address as the mobile communication terminals 10 and 11 are in motion.
FIG. 2 is a conceptual diagram illustrating a handover process for use in the above-mentioned portable Internet system. A handover process for use in the portable Internet system according to a related art will hereinafter be described with reference to FIG. 2.
Referring to FIG. 2, the mobile communication terminal 10 transmits a handover request (Ho/REQ) message acting as a media access control (MAC) message to the base station 20 in order to perform a handover. Upon receiving the handover request message from the mobile communication terminal 10, the base station 20 determines whether neighbor base stations can accommodate the handover request of the mobile communication terminal 10 by exchanging subscriber and/or terminal information, and configures the list of at least one neighbor base station capable of accommodating the handover request in the form of a handover response message, such that it transmits the handover response (HO/RSP) message to the mobile communication terminal 10.
The mobile communication terminal 10 receives the handover response (HO/RSP) message, selects a single neighbor base station (e.g., base station 21) among the recommended neighbor base stations, informs the base station 20 of the selected neighbor base station 21, and attempts to enter the network of the selected neighbor base station 21. In the meantime, the handover can also be performed although the base station 20 firstly transmits the handover request message to the mobile communication terminal 10.
FIG. 3 is a flow chart illustrating a handover request procedure of the portable Internet system according to a related art.
Referring to FIG. 3, the mobile communication terminal 10 performs quickly a handover from a current base station (e.g., base station 20) to another base station (e.g., base station 21) via a simplified procedure easier than the initial network access procedure.
As shown in FIG. 3, a handover requested by the mobile communication terminal may be rejected by the base station currently communicating with the mobile communication terminal for various reasons. In this case, the mobile communication terminal requires a specific procedure capable of stably communicating with the portable Internet system. However, the specific procedure is not defined in the portable Internet standard according to the related art.